1. Field of the Invention
The invention pertains to a method for verifying the consistency of the sideslip probes of an aircraft and to a device implementing this method.
2. Discussion of Prior Art
The piloting of any aircraft requires a knowledge of its relative speed with respect to the air, that is to say to the relative wind. This speed is determined with the aid of sensors of static pressure Ps, of the total pressure Pt, of the angle of incidence α and of the angle of sideslip β.
The angle of incidence α of an aircraft is commonly defined as being the angle of the air speed vector with respect to a horizontal plane of the aircraft. Likewise, the angle of sideslip β of an aircraft is defined as being the angle of the air speed vector with respect to a vertical plane, generally a symmetry plane, of the aircraft.
The values of α and of β are conventionally estimated by known techniques, for example on the basis of a measurement of the pressure of the air outside the craft, as is the case in patent EP 1 354 212 B1. These pressure measurements are taken by probes arranged on the surfaces of the aeroplane. These probes can be of the Pitot or multifunction type (MFP).
Sideslip probes which do not use the measurement of the pressure are beginning to be used on civil aeroplanes. These probes dispatch an electrical signal as a function of time, indicative of the locally measured sideslip angle.
Sets of such probes with so-called weathervanes, also dubbed fins, generally comprise three probes fitted on the nose of the craft. The arrangement of such a set on an aircraft is illustrated in FIG. 3.
In this figure, the central plane X of the craft C is the symmetry plane of the fuselage, coinciding with the plane of the rudder. The probes 1, 2, 3 are arranged on the nose of the craft C, the two probes 1, 2 being symmetrically situated on either side of the plane X and the probe 3 being situated in the plane X. The three probes 1,2,3 are substantially aligned along a straight line Y perpendicular to the plane X of the aeroplane. This system of three probes is generally situated on the nose Cp of the craft C.
In probes of the weathervane type, it is difficult to detect a failure of the probe due to the deformation or displacement of the weathervane. FIG. 1 represents such a type of weathervane probe. The weathervane G overhangs the base S which is fitted in the fuselage. It is understood that the weathervane G is a sensitive part of the probe since it is subjected to the exterior environment.
It is known from patent EP 1 354 212 B1 to verify the consistency between three measurement probes by applying the triplex principle.
According to this principle, it is possible to note a defect on a measurement pathway when one of the probes of this pathway gives a very different result from the other two. It is then deduced therefrom that this pathway is defective. Nonetheless, within this pathway, the defective probe remains indeterminate.
The triplex principle is illustrated in FIG. 2. In FIG. 2a, the probes 2 and 3 indicate an angular sideslip value of 3° for probe 2 and of 3.1° for probe 3. Probe 1 gives for its part a value of 8° very different from the others. The measurements of probe 1 are therefore rejected.
In other cases, the application of the triplex principle may in particular turn out to be insufficient. Indeed, when two probes give erroneous but mutually consistent information, the correct measurement is rejected. This case is illustrated in FIG. 2b. Probe 1 gives a value of 8° and probe 3 gives a value of 8.1°. This information is erroneous but mutually consistent. Probe 2 gives a value of 3°, this in fact being the correct value of sideslip angle, but the application of the triplex principle means that it is the measurements of this probe 2 which are rejected.
It is therefore necessary to know whether the information given by the sideslip probes is correct, so as to indicate to the computer whether or not it may take this information into account.
A first solution consists in arranging a greater number of probes than that necessary for the measurements or else in installing a system of additional checking probes as is described in patent EP 1 354 212. However, these solutions lead to difficulties of integrating these systems into aeroplanes.
A second solution consists in estimating the value of the sideslip and in comparing the estimated value with the measured value so as to detect errors, if any, which may arise subsequent to the sole application of the triplex principle. This solution is effective and is generally employed on craft of modern design. In order to further increase flight safety, provision may be made to supplement this solution with means for verifying the consistency of the measurements of the sideslip probes.
One of the objectives of the invention is to provide a system for verifying the consistency of the sideslip probes which does not require the installation of additional probes.